页岩气水力压裂过程中水泥环裂缝扩展规律研究

Study on the Fracture Propagation Mechanisms of Cement Sheath during Shale Gas Hydraulic Fracturing

摘要: 为了提升页岩气井完井固井质量并保障压裂作业安全，对水力压裂过程中水泥环裂缝扩展规律进行了系统研究。鉴于水泥环在保障系统完整性、井壁稳定性和压裂效果中的关键作用，分析了温度应力场对组合体力学行为的影响机制。揭示了水泥环厚度、水泥环弹性模量、水泥环泊松比对其自身应力状态的调控规律，深入探讨水泥环在不同应力状态下的裂缝扩展规律。并且基于多物理场耦合理论，通过分析理论建模与实验验证相结合的模拟结果，提出了基于粘聚力模型(CZM)的裂缝扩展预测方法，实现了压裂过程中水泥环损伤演化的精确模拟。同时构建了包含温度–应力–渗流多场耦合的数值分析体系，开发了适用于复杂地质条件的裂缝扩展预测模型。研究成果为优化固井工艺参数与井筒完整性保障提供了理论依据，并展望了高温高压环境下多尺度模拟与智能监测技术的发展方向，对页岩气安全高效开发具有一定的指导意义。

Abstract: To improve the quality of well completion and cementing for shale gas wells and ensure the safety of fracturing operations, this study conducts a systematic research on the crack propagation law of the cement sheath during hydraulic fracturing. Given the critical role of the cement sheath in ensuring system integrity, wellbore stability, and fracturing effectiveness, it analyzes the influence mechanism of the thermal stress field on the mechanical behavior of the composite system. It reveals the regulatory laws of cement sheath thickness, cement sheath elastic modulus, and cement sheath Poisson's ratio on its own stress state, and explores in depth the crack propagation law of the cement sheath under different stress states. Furthermore, based on the multi-physics field coupling theory, by analyzing the simulation results combining theoretical modeling and experimental verification, a crack propagation prediction method based on the Cohesive Zone Model (CZM) is proposed, which realizes the accurate simulation of cement sheath damage evolution during fracturing. Meanwhile, a numerical analysis system involving temperature-stress-seepage multi-field coupling is constructed, and a crack propagation prediction model suitable for complex geological conditions is developed. The research findings provide a theoretical basis for optimizing cementing process parameters and ensuring wellbore integrity, and prospect the development direction of multi-scale simulation and intelligent monitoring technology under high-temperature and high-pressure environments, which have certain guiding significance for the safe and efficient development of shale gas.